Na order and Co charge disproportionation in NaxCoO2

作者：Mukhamedshin I R^*; Alloul H

来源：Physica B: Condensed Matter , 2015, 460: 58-63.

DOI：10.1016/j.pkvsb.2014.11.040

• Layered oxides
• Magnetic resonance
• Charge order

We have synthesized and characterized different stable phases of sodium cobaltates NaxCoO2 with sodium content 0.65 < x < 0.80. We demonstrate that Na-23 NMR allows us to determine the difference in the susceptibility of the phases and reveals the presence of Na order in each phase. Co-59 NMR experiments give clear evidence that Co charge disproportionation is a dominant feature of Na cobaltates. Only a small fraction (approximate to 25%) of cobalt are in a non-magnetic Co3+ charge state whereas electrons delocalize on the other cobalt. The magnetic and charge properties of the different Co sites are highly correlated with each other as their magnetic shift K-ZZ scales linearly with their quadrupolar frequency v(Q). This reflects the fact that the hole content on the Co orbitals varies from site to site. The unusual charge differentiation found in this system calls for better theoretical understanding of the incidence of the Na atomic order on the electronic structures of these compounds.

• 出版日期2015-3-1